This invention relates to improvements in the construction of radial piston hydraulic pumps and motors and, in particular, to the mounting of the pintle shaft so that it remains stable and essentially vibration free, thus reducing wear and noise and increasing efficiency.
U.S. Pat. No. 3,771,423, issued Nov. 13, 1973, for "Radial Pump or Motor With Stabilized Pintle" describes and shows radial piston hydraulic pump-motors having cantilevered pintle shafts and various mechanical devices for supporting the blind end of the pintle shaft against side loads. For various reasons it is advantageous to mount the pintle shaft at one end on a frame member as in the pump-motor described in that patent. However, the fact that the pintle shaft of such a pump-motor is mounted to be moved laterally for torque and speed control causes some problems.
The pump-motor of the aforementioned patent comprises a pair of end frame members, the pintle shaft being cantilevered from and mounted to slide laterally on one, and the reaction assembly being journaled by way of the input-output shaft on the other. The reaction assembly includes a pair of reaction rings, one on either side of the cylinder block, each of which is connected to each piston by one or more Scott-Russell linkages (see U.S. Pat. No. 3,709,104 issued Jan. 9, 1973 for "Radial Piston Hydraulic Pump or Motor With Low Loss Reaction Linkage"). The Scott-Russell linkages eliminate all side loads on the pistons; accordingly, each piston exerts or is subject to only a radial force. For example, in the motor mode, the hydraulic fluid delivered to the cylinders on the charge or high pressure side produces radially outward forces on the corresponding pistons, and the reaction assembly imposes radially inward forces on the pistons on the discharge or low pressure side. For purposes of analyzing the loads on the pintle shaft (as distinguished from a full analysis of the stresses on the pintle shaft which involves consideration of the hydrostatic pressure in the pintle) the radially acting and reacting forces on the pistons can be resolved into components acting (1) perpendicular to the plane of lateral movement or adjusting translation of the pintle shaft (i.e., components perpendicular to the pintle bridge and hereinafter referred to as "perpendicular loads") and (2) parallel to the plane of adjusting translation (hereinafter called "side loads"). The perpendicular loads are unidirectional from the high pressure side toward the low pressure side in any given mode of operation of the pump-motor and are generally of the order of roughly two to five times the maximum side loads, depending primarily upon the number of cylinders, the cylinder diameters and the widths of the land areas of the pintle bridge. The side loads are cyclical in magnitude and direction, the number of cycles of load change per revolution being equal to the number of cylinders.
In the pump-motors of U.S. Pat. No. 3,771,423, the reaction assembly has a bearing adjacent the blind end of the pintle shaft, and a pair of slide pins on the pintle shaft are received in a slot in that bearing, thus permitting the pintle shaft to be adjusted laterally. The pins transfer part of the perpendicular loads between the pintle shaft and the reaction assembly but afford very little transfer of side loads between the pintle shaft and reaction assembly. Accordingly, the pintle shaft is subject to oscillatory rocking in the lateral direction, and one or another form of mechanical restraining system is provided to stabilize the pintle shaft against rocking.
The reaction ring at the outside end of the aforementioned pump-motor, i.e., at the end where the pintle shaft is mounted, is carried by a bearing that is affixed to the outside end frame member. Both perpendicular and side loads on that reaction ring are, therefore, transferred to the frame. Meanwhile, the part of the perpendicular load on the pintle shaft not transferred between the pins at the blind end and the slotted bearing is carried by the cantilever mounting, thus requiring the housing or frame to be strongly built to a precision that will ensure proper alignment between the axes of the pintle shaft and reaction assembly. But for the stabilizing mechanisms at the blind end of the pintle shaft, which support the blind end against the cyclical side loads, the cantilever mounting structure would be subject to forces tending to cock the shaft out of line. The cantilever support structure is, however, subject to part of the side loads on the pintle shaft, such part being imposed on the pintle shaft adjusting mechanism.